Automatic inspector of the surface of running object

ABSTRACT

An apparatus for detecting defects in the surface of a running sheet material by continually scanning it in the transverse direction; wherein the running speed of the sheet object is detected, the amount of electricity proportional to the running speed is integrated by an integrator over the period of time for which the surface of the running sheet object is scanned by the light beam, the output of the integrator is converted into a plurality of pulses with different rise points by a comparator circuit including a plurality of comparator units for comparing the output of the integrator with a predetermined level, these pulses and a signal obtained as a result of the running object being scanned by a light beam are digitally processed by a digital processor thereby to convert them into a group of divided pulses of which the rise point of one occurs at the same time as the fall point of an adjacent pulse, and defect detection signals obtained by light-beam scanning of the object are recorded in sequence by a plurality of recorders corresponding to said divided pulses.

United States Patent 11 1 Kaneko et al.

[ Nov. 20, 1973 AUTOMATIC INSPECTOR OF THE SURFACE OF RUNNING OBJECTPrimary ExaminerJames W. Lawrence Assistant Examiner-D. C. Nelms 75Inventors: Aklra Kaneko Kokubun 1; Yutaka l Nagam Kodaira, both JapanAttorney-Paul M. Craig, Jr. et a]. [73] Assignees: Hitachi ElectronicsCo., Ltd.; [57] ABSTRACT Nlsshm steel Tokyo An apparatus for detectingdefects in the surface of a Japan running sheet material by continuallyscanning it in 22 i Aug 24, 1972 the transverse direction; wherein therunning speed of the sheet object is detected, the amount of electricity[21] Appl' 283395 proportional to the running speed is integrated by anintegrator over the period of time for which the sur- 3( F i li i P i iData face of the running sheet object is scanned by the light Aug 251971 Japan 46/64362 beam, the output of the integrator is converted intoa Aug 1971 Japan 46/6436? plurality of pulses with different rise pointsby a comarator circuit including a lurality of com arator p a 0 p I p I[52] CL "2505) 250,219 wEL356/200 units for comparing the output of themtegrator with a 511 110. C1. semi/3o predetemmed level, these PulsesSignal [58] Field of Search 250/209, 214, 219 DF, as a result E b1ect250/219 WE, 219 WD 221, 222 234 235, by a light beam are digitallyprocessed by a d1g1tal pro- 356/199 200 202 237 cessor thereby toconvert them into a group of divided pulses of which the rise point ofone occurs at the [56] References Cited same time as the fall point ofan adjacent pulse, and

defect detection signals obtained by light-beam scan- UNITED STATESPATENTS ning of the object are recorded in sequence by a plui; i f 2 5632 0 rality of recorders corresponding to said divided o nson 3,558,9001/1971 Moskowitz.. 250 219 DF pulses 3,158,748 11/1964 Laycak 250/219 WE2 Claims, 4 Drawing I A 9 11 W s C (J UFFERENI'IATING II.J I50 01 CIRCUTGDMPARATOR BA 2 COUNTER HI v' R A MP. GATE COUNTER IO m 9 WAVE O SHAPINGCIRCUIT COUNTER 14 E GC i PULSE DIGITAL DIVIDING PROCESSING CIRCUITCIRCUIT l -FG I' -F PAIENIEDHHY 20 ms 3,77

- saw 10; 3

PMENIEDIIIIII 20 I975 3.7 74. O4 1 SHEET 2 BF 3 F I G 2 I' I A 9 II M ad C DFFERBVTIATING M c CIRCUW ooMPARAToR 5i 8% 2 COUNTER IM R l5b GATECOUNTER IO WAVEFORMKN P SHAPING m JLGQ l4 l3 J'L I Gc PULSE DIGITAL iDIVIDING PROCESSING CIRCUIT CIRCUIT mFo PAIENIEDnuvzmsn 3,774.04}

SHEET 3 [IF 3 F l G 3 8 I8 20 \x v f gg'g ERROR REVOLUTIONS DETECTOR[HECTOR DETECTOR |7- MOTOR CONVERTER CONTROLLER cONvERTER 24 wINTEGRATING 22* |NTEGRATOR 23 TIME COMPARATUR SETTING SIGNAL GENERATOR Fl G 4 I K27 28 ANALOG VALUE INTEGRATOR ax 29 GENERATOR I -1 DATA --Q I30 r3 II PROCESSOR I INTEGRATOR COMPARATOR AUTOMATIC INSPECTOR OF THESURFACE OF RUNNING OBJECT BACKGROUND OF THE INVENTION l. Field of theInvention This invention relates to an apparatus for automaticallyinspecting the surface of a running object, or more in particular to anapparatus for detecting defects such as unevenesses flaws or variationsin luster on the surface of a metal plate, paper and plastic sheet whilethey are being processed.

2. Description of the Prior Art A conventional device for detecting adefect on the surface of a running sheet object is known in which thesurface of the object is scanned by a beam of light and the lightreflected therefrom is used to find where a defect, if any, is locatedamong a plurality of portions into which the running object is dividedin the longitudinal direction. This conventional device, however, doesnot operate accurately in accordance with the changes in the runningspeed of the object.

SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to provide an automatic defect inspecting apparatus whoseoperation is not adversely affected by changes in the running speed ofthe object and in which the surface of a running object is scanned byflying spots of light, the light reflected from the surface of theobject is converted into an electrical signal by a light-receivingsystem, a defect, if any, on the surface of the object is detected inthe form of a variation in the electrical signal, and the portion of theobject is found where the detected defect is located among a pluralityof portions into which the object is divided in the longitudinaldirection.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showinga perspective view of the automatic defect inspector according to thepresent invention.

FIG. 2 is a block diagram showing a conventional defect inspector.

FIGS. 3 and 4 are block diagrams showing the apparatus according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, thereference numeral 1 shows an object to be inspected which runs in thedirection of the arrow, numeral 2 a beam of light generated from a lightsource including an incandescent lamp, mercury lamp or laser, andnumeral 3 a rotary reflector consisting of a polygonal pole rotated by adriving means 4 and which reflects the light beam for continuallyscanning the surface of the object 1 in the transverse direction.Numeral 5 shows a locus of the scanning light beam. Numeral 6 shows aconverter for converting the light beam 2 reflected from the surface ofthe object into an electrical pulse, and numeral 7 a second converterwhich directly receives the light beam 2, not after reflection on thesurface of the onject, and which is placed at such a position where thelight beam 2 is just to begin the scanning operation. Numeral 8 shows adevice for detecting the speed of the running object 1. Where adefect,if any, detected by the converter 6 in the form of an electrical signalis located among the plurality of portions into which the object 1 wasdivided is known by a plurality of counter which are so arranged as torecord electrical signals corresponding to the divided portions of theobject 1.

Explanation will be made now of an embodiment in which the object 1 isdivided into three portions in the longitudinal direction for thescanning purpose.

In FIG. 2, the electrical signal A with a pulse width equal to atransverse scanning time T is applied to the differentiating circuit 9and wave-form shaping circuit 10. The differentiated signal B is changedby the comparator 11 into a defect signal C representing a defect, ifany, with a magnitude not lower than a certain level, the signal C beingapplied to the gate 12. On the other hand, the electrical signal Aapplied to the wave-form shaping circuit 10 is transformed into a shapedpulse D with a pulse width equal to the duration of the scanning by thelight beam 2 over the object 1. The shaped pulse D thus representing thewidth of the band-plate object is applied to the digital processingcircuit 13. The electrical signal E from the converter 7 which directlyreceives the light beam 2 immediately before it begins to scan theobject 1 is applied to a pulse dividing circuit 14 in the form of atrigger pulse. The pulse dividing circuit 14 produces three pulses Fa,Pb and Fe with differ ent rise points, The pulses Fa, Pb and Fe beingapplied to the digital processing circuit 13. In the digital processingcircuit 13, the shaped pulse D representing the width of the band-plateobject and the three pulses Fa, Fb and P0 with different rise pointscombine to produce three pulses Ga, Gb and Gc representing the threedivided portions of the object and having staggered rise and fallpoints, the rise point of one pulse occurring at the same time as thefall point of an adjacent pulse. The gate 12 to which the pulses Ga, Gband G0 are applied in followed by the stage in which the counters 15a,15b and 15c corresponding to the pulses Ga, Gb and Ge respectivelyrecord the defect signal C from the comparator 11 which represents adefect with a magnitude higher than a certain level. In this way, it ispossible to find which portion of the object contains the defect bydetermining the pulses G a, Gb, and Ge so as to be indicative of thedivided portions of the object, respectively. In this device, at thebeginning and/or end of the scanning by the light beam 2 the edges ofthe object are possibly the false detected as defects thereby producingfalse signals. This may be prevented by providing a delay circuit foradjusting the pulse widths.

Hitherto, a delay circuit including three delay units has been employedfor producing the divided pulses. In that case, however, the scanningspeed of the light beam 2 is required to vary with the running speed ofthe object 1, resulting in the variation in the width of the shapedpulse D which is an output of the waveform shaping circuit 10representing the width of the sheet object. This caused the width of thepulses Ga, Gb and G0 to change. Therefore, it is required to change therising points of the three pulses Fa, Fb and Fe by changing the delaytimes of the delay units in order to provide the pulses Ga, Gb, and G0with suitable widths. However, it is practically very difficult tosatisfy such requirement.

This invention, which makes it easy to get the divided pulses inaccordance with any change in the running speed of the object 1, will beexplained in more detail with reference to the accompanying drawings.Referring to FIG. 3, the reference numeral 8 shows a device fordetecting the running speed of the object 1, numeral 17 a D-A converter,numeral 18 an error detector circuit, numeral 19 a controller of themotor driving the rotary reflector 3, numeral 20 a revolutionsdetectingsection of the rotary reflector 3, numeral 21 a D-A converter, numeral22 an integrator, numeral 23 a comparator circuit and numeral 24 acircuit for generating signals which determine the period of time overwhich the integrating operation is performed by the integrator 22. Therunning speed of the object 1 is detected by the running speed detector2 in the form of a pulse signal of a frequency proportional thereto,which signal is converted into an analog value by the D-A converter 17.This signal representing the running speed of the object 1 controls themotor control section 19 through the error detector circuit 18 so thatthe revolutions of the rotary reflector 3 are changed in proportion tothe running speed of the object 1. The revolutions of the rotaryreflector 3 are detected by the revolutions detecting section 20 in theform of a digital value which is fed back to the error detector circuit18 to regulate the revolutions. In this system of feedback control, theoutput of the D-A converter 21 which is proportional to the runningspeed of the object 1 is integrated by the integrator 22 to obtain theequation where E, is the output voltage of integrator 22, T the timeconstant of the integrator 22, 'r the output voltage of the D-Aconverter 21 which is proportional to the running speed of the objectand T an integrating time which means a period of time over which thelight beam 2 scans the surface of the object 1 once in the transversedirection. This time T is determined by the integrating time settingsignal generator circuit 24 and is expressed as T= l/ V, where l is thewidth of the bandplate object and V the scanning speed. Since therunning speed of the object 1 is proportional to the scanning speed ofthe light beam 2, E, kl/r (k: a proportional constant), indicating thatthe output voltage of the integrator gradually increases from nil to Eafter time T where it is proportional to the width of the bandplateobject without regard to the running speed thereof. The output of theintegrator 22 is applied to the comparator circuit 23 including aplurality of comparator units for producing pulses which respectivelyhave rise points at different voltage levels. These pulses correspond tothe output signal of the delay circuit of the conventional device, andtherefore application of the output of the comparator circuit 23 to thedigital processing unit permits production of pulses corresponding tothe divided portions of the band-plate object 1 without being affectedin any way by the running speed of the object 1. Although the aboveexplanation of the invention involves the integration of an analog valueproportional to the running speed of the object 1, the integration of adigital value may apply to the device of the invention with same degreeof effect.

The integrating time T which is determined by the integrating timesetting signal generator circuit 24 may be obtained either by erasingdefect-carrying signals as a result of slicing an electrical signal fromthe converter 6 or by the output signals of such photoelectric elementsas photo transistors disposed on both side edges of the object 1. In theformer case, an error results when a defect on the surface of the object1 is so large that the defect signal cannot be erased by the slicing ofthe output signal of the converter 6, while in the latter case a changein the width of the band-plate object 1 results in the inconvenience ofthe need for relocating the photoelectric elements although themagnitude of a defect does not affect the accuracy of detection. Toovercome these difficulties, the embodiment of FIG. 4 is designed tolocate a defect easily without regard to the magnitude thereof and achange in the width of the object 1.

The embodiment of the invention will be now explained with reference toFIG. 4. The reference numeral 26 shows an analog value-signal generatorcircuit, numeral 27 an integrator, numeral 28 a dividing gate circuitand numeral 29 a data processing unit which operates in the same way asthe conventional device. Numeral 30 shows a second integrator, andnumeral 31 a comparator with a reference voltage set therein whichgenerates a reset signal when its input voltage reaches the level of thereference voltage. Also, the reference voltage is adapted to vary withthe width of the band-plate object 1. As soon as an electrical signal isproduced from the converter 6 after the scanning is started by the lightbeam 2, the integrators 27 and 30 start to integrate the analog value inproportion to the running speed of the object which is obtained from theanalog signal generator circuit 26. Under this condition, there is arelation where E is the output voltage of the integrator 27, r, the timeconstant thereof, T an integrating time, and u an input voltageproportional to the running speed of the object 1. Also,

where E is the output voltage of the integrator 30, r the time constantthereof, T an integrating time, and v an input voltage. The output ofthe integrator 30 is applied to the comparator 31 so that when theoutput of the integrator 30 reaches the level of the reference voltageof the comparator 31, the comparator 31 produces a reset signal forresetting the integrators 27 and 30. Therefore, the integrating time Tcontinues from the instant when a signal due to the light beam 2 appearsin the converter 6 to the time point when the output voltage of theintegrator 30 reaches the level of the reference voltage of thecomparator 31. The output of the integrator 27 is applied to thedividing gate circuit 28. In this case, it is desirable to maintain theoutput voltage constant for different integrating times, if a defeet isto be easily located.

For this purpose, the time constant of the integrator 27 should beadapted to change in proportion to the reference voltage of thecomparator 31. Since as will be understood from equation (1) the timeconstant and integrating time are proportional to each other, anincrease in the reference voltage due to a greater width of theband-plate object results in a proportionately larger time constant ofthe integrator 27, thereby lengthening the period of time before theintegrator 27 reaches a certain level of operation. A higher referencevoltage lengthens the period of time before the output voltage of theintegrator 30 reaches the reference voltage, thus lengtheningtheintegrating time T, with the result that the output voltage of theintegrator 27 is maintained constant without regard to the width of thesheet object.

As will be apparent from the above explaination, the accuracy ofdetection of the apparatus according to the present invention isaffected by neither the running speed of the object to be inspected nora large defect. Further, a defect, if any, can be easily located bychanging the reference voltage even if the width of the sheet objectchanges.

We claim:

1. In an apparatus for detecting a defect on the surface of a runningsheet object by applying a beam of light onto the surface of said objectfor the scanning thereof in the transverse direction, the improvementcomprising means for detecting the running speed of said object, meansfor integrating the amount of electricity proportional to said runningspeed over a period of time needed for said beam of light to scan saidsurface of said object, a comparator including a plurality of comparatorunits for comparing the output of said integrating means withpredetermined different reference levels and converting said output ofsaid integrating means into a plurality of pulses with different risepoints, digital processing means for converting said pulses and a signalobtained from the scanning of said surface of said object into 'aplurality of pulses having staggered rise and fall points, the risepoint of one pulse occurring at the same time as the fall point of anobject pulse and a plurality of recording means which are energizedrespectively in response to said converted pulses, said recording meansrecording in sequence defect-carrying signals obtained by the scanning.

2. In an apparatus for detecting a defect on the surface of a runningsheet object by applying a beam of light onto the surface of said objectfor the scanning thereof, the improvement comprising means for detectinga voltage proportional to the running speed of said object, a couple ofintegrators which begins to integrate said voltage the instant that saidbeam of light begins to scan the surface of said object, a comparatorwhich produces a reset signal when the output of one of said integratorsreaches the level of the reference voltage of said comparator which isvariable according to the width of said object, said integrator beingreset by said reset signal, a gate circuit for producing a plurality ofdivided pulses in response to the output of the other of saidintegrators which has a time constant variable with said referencevoltage, each of said divided pulses having a rise point occurring atthe same time as the fall point of an adjacent divided pulse, aplurality of recording means corresponding to and energized respectivelyby said divided pulses, said recording means recording in sequencedefect-carrying signals obtained by the scanning of said surface of saidobject.

1. In an apparatus for detecting a defect on the surface of a runningsheet object by applying a beam of light onto the surface of said objectfor the scanning thereof in the transverse direction, the improvementcomprising means for detecting the running speed of said object, meansfor integrating the amount of electricity proportional to said runningspeed over a period of time needed for said beam of light to scan saidsurface of said object, a comparator including a plurality of comparatorunits for comparing the output of said integrating means withpredetermined different reference levels and converting said output ofsaid integrating means into a plurality of pulses with different risepoints, digital processing means for converting said pulses and a signalobtained from the scanning of said surface of said object into aplurality of pulses having staggered rise and fall points, the risepoint of one pulse occurring at the same time as the fall point of anobject pulse and a plurality of recording means which are energizedrespectively in response to said converted pulses, said recording meansrecording in sequence defect-carrying signals obtained by the scanning.2. In an apparatus for detecting a defect on the surface of a runningsheet object by applying a beam of light onto the surface of said objectfor the scanning thereof, the improvement comprising means for detectinga voltage proportional to the running speed of said object, a couple ofintegrators which begins to integrate said voltage the instant that saidbeam of light begins to scan the surface of said object, a comparatorwhich produces a reset signal when the output of one of said integratorsreaches the level of the reference voltage of said comparator which isvariable according to the width of said object, said integrator beingreset by said reset signal, a gate circuit for producing a plurality ofdivided pulses in response to the output of the other of saidintegrators which has a time constant variable with said referencevoltage, each of said divided pulses having a rise point occurring atthe same time as the fall point of an adjacent divided pulse, aplurality of recording means corresponding to and energized respectivelyby said divided pulses, said recording means recording in sequencedefect-carrying signals obtained by the scanning of said surface of saidobject.